Functionalized particles for composite sensors

ABSTRACT

A chemical sensor having a transducer element and a layer of composite material including a polymer matrix and a solid particulate filler disposed in the polymer matrix provides chemical sensors exhibiting improved properties. In particular, the device allows polymer matrix materials to be selected based primarily on diffusion properties, strength, stability and other physical characteristics substantially independent of limitations and compromises that arise when attempting to synthesize polymers having specific types of sensory groups chemically bound to the polymer. The invention also allows greater ability to modify sensor response characteristics by appropriate modification of the particulate filler, whereby a diverse sensor array may be fabricated more easily and at a lower cost.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/694,027, entitled “FUNCTIONALIZED PARTICLES FOR COMPOSITE SENSORS”,filed Oct. 27, 2003, the entire disclosure of which is incorporatedherein by reference.

FIELD OF THE INVENTION

This invention relates to chemical sensing devices, and moreparticularly to the use of composite materials for sensing chemicalvapors.

BACKGROUND OF THE INVENTION

Chemical vapor sensing instruments are expected to become increasinglyimportant in a variety of applications, including industrial hygiene,environmental clean-up, national defense and homeland security. Improvedtechnology to reliably detect and identify potentially toxic orexplosive volatile organic compounds is critically needed for theseapplications.

Many different approaches are being developed and refined throughout theacademic, government and industrial/commercial research and developmentorganizations. Current efforts have focused primarily on improving theportability of traditional analytical instruments such as gaschromatographs and optical spectrometers, and improving the sensitivityand reliability of array-based chemical sensors that measuregravametric, optical or electromechanical properties. The array-basedchemical sensors are favored when low cost, portability, ease ofoperation and ease of maintenance are desired.

A sealed-deployable sensor system must be able to unambiguously detectan analyte of concern and provide an accurate measurement of the analyteof concern regardless of the presence of chemically similar interferingcompounds. The most successful field-deployable sensor systems utilizecross-reactive chemical sensor arrays in which individual sensingelements are coated with materials that respond to broad classes ofchemical vapors, with each sensor material being chosen to besufficiently different from the other sensor materials so that thecollective array of sensors will span a broad range of possible chemicalproperties.

A variety of organic, inorganic and organometallic materials have beentested as sensor materials. Notable examples include self-assembledmonolayers, Langmuir-Blodgett films, clathrates, small organic moleculesand polymers. Most functional commercial and/or prototype vapor sensinginstruments use arrays of polymer-coated sensing elements. This isbecause polymer coatings can be selected to exhibit excellent sorptiveproperties for organic vapors, rapid diffusion if the polymer is aboveits glass-to-rubber transition temperature, reversible responses, andlinear sorption isotherms over a large concentration range for lowpolarity vapors. The sensor coating materials may be selected to achievea wide range of selectivities, such as by synthetic variation of thepolymer structure.

In addition to the above properties, it is highly desirable thatsensor-coating materials possess excellent processing characteristics.Specifically, mass production of reliable and inexpensive vapor sensingdevices will require sensor-coating materials that are readilyprocessable into thin, adherent films.

There are many polymers available that meet many of these requirementsand offer other advantages. In particular, polymers can be made with awide variety of functional groups (e.g., sensing groups) that may beincorporated directly into the polymer backbone during synthesis orappended to the polymer backbone after synthesis. Polymers may also beselected for a particular application based on appropriate molecularcompositions and/or molecular architectures. Polymers may also be chosenbased on the ability to cross-link, graft to substrates, or both. Manytypes of polymers are amorphous, i.e., either not crystalline orpartially crystalline. Such polymers tend to be either rubbery or glassyand exhibit absorptive properties that may be advantageously employedfor vapor sensing applications. Another advantage with using polymersfor vapor sensing applications is that many polymers exhibit excellentstability and very low volatility at ambient conditions and/or elevatedtemperatures. Further, most polymers are easily processed into a varietyof different forms. However, it is not easy to develop a simple polymerthat will exhibit a combination of all these desired properties.

It is generally necessary and desirable to use an array of differentsensors in a vapor-sensing device since it is impossible to achieveperfectly selective detection of any particular analyte using a singlesensor. Any particular sensor will typically respond to severaldifferent analytes. However, any given sensor may respond to aparticular set of analytes including some, but not all, of the analytesdetectable by another sensor. Using a suitable array of sensors, it ispossible to identify a single analyte based on a determination of theparticular sensors in the array that respond to the analyte. Byemploying suitable calibration techniques, it may be possible to achievequantitative analysis for a single analyte, and qualitative orquantitative analysis for a plurality of different analytes.

While vapor sensing devices employing an array of different sensors aregenerally required to achieve highly selective detection, it isdesirable to use only a few different types of base polymers, and morepreferably a single type of base polymer, for each of the sensors in thearray, and modify the individual members of the array with differentfunctional groups (sensing groups) to achieve a desired array ofselective responses. This provides a simplified production process ascompared with using a completely different polymer for each member ofthe array. However, polymers with every conceivable type of functionalgroup are generally commercially unavailable. For example, polymers withhydrogen bond acidic functionalities, which would be useful forselective detection of hydrogen bond basic analytes such as chemicalwarfare nerve agents and explosives, and which otherwise meet therequirements for polymer detectors, are generally commerciallyunavailable.

There are currently three common categories of commercially availablechemical vapor sensing devices utilizing polymer-coated sensingelements. A first category is devices comprising an array of acousticwave sensors using quartz crystal microbalances (QCM), surface acousticwave (SAW) devices, or flexural plate wave (STW) devices as the sensingtransducers. For acoustic wave sensors, the generated signals areproportional to the mass of the vapor sorbed by each polymer coating onthe surfaces of the device. A second category of commercially availablearray-based chemical sensors utilizes a chemiresistor transducercomprising an insulating polymer that is loaded with electricallyconductive particles. In this device, vapor sorption swells theinsulating polymer and increases the resistance through thepolymer-conducting particle composite. Lastly, the third common categoryof commercially available array-based chemical sensors employs a sorbentpolymer as the matrix for fluorescent dyes, such as Nile red. Vaporsorption alters the fluorescence signal from the incorporated dyemolecules. In a minor variation of this, arrays have been prepared withvarious dyes in various polymers on the ends of fiber-optic bundles. Itis also conceivable that a chemical vapor sensing apparatus could employany combination of these three types of sensors.

The task of choosing and optimizing a chemically diverse array ofpolymer-coated sensing elements can be rationally accomplished throughthe use of solubility interactions and linear solvation energyrelationships. It is believed that a sorbent polymer-based sensor arraywill collect the most chemical information if the polymer coatings inthe array cover the full range of solubility interactions, includingdispersion, dipole-dipole, and hydrogen-bond interactions. This approachrequires a variety of different polymer coatings, including non-polar,polarizable, dipolar, hydrogen bond basic, and hydrogen bond acidic.Many polymer coatings exhibiting these types of solubility interactionsare well known and commercially available, with the notable exception ofthe hydrogen bond acidic polymers. This presents a problem for at leasttwo critically important applications for chemical vapor sensingapparatuses employing polymer-coated sensing elements. In particular,there is a need for the development of hydrogen bond acidicpolymer-coated sensors for detection of nerve agents and explosives. Inaddition, there is a need for the development of hydrogen bond acidicpolymer coatings to expand the chemical diversity of a sensor array,thus helping to optimize its ability to discriminate between variousclasses of vapors.

A large body of research on surface acoustic wave devices hasdemonstrated that incorporation of highly fluorinated alcoholic orphenolic functional groups into the sensing polymers is an effective wayof maximizing hydrogen bond acidity. Concomitant minimization ofbasicity reduces the extent and strength of self-association, whichwould otherwise tend to lessen the driving force for interaction withbasic vapors. Self-association is a major drawback to the use ofcarboxylic acid functional groups, which are good hydrogen-bond acids asmonomers, but nearly always self-associate when in a condensed phase.

Strongly hydrogen bond acidic polymers also have intrinsically highpolarity. Although this is a desirable feature in terms of chemicalsensitivity, it poses a potential problem because highly polar functiongroups on polymers lead to higher glass-to-rubber transitiontemperatures than those of corresponding nonpolar polymers. Polymershaving a glass-to-rubber transition temperature near or above roomtemperature (about 22° C.) typically act as diffusion barriers andprovide unacceptably slow response times when used as coatings forchemical sensors.

SUMMARY OF THE INVENTION

The invention provides composite chemical sensing materials that exhibitexcellent mechanical properties, and more strength and better agingperformance than conventional polymer sensor materials in which thesensor groups are part of the chemical structure of the polymer. Thechemical sensing composite materials of this invention include a matrixpolymer having a low glass transition temperature, typically at or belowroom temperature (about 22° C.), and exhibit good diffusion propertiesand good response times on contact with chemical vapors. The chemicalsensing composite materials of this invention include a polymer matrix,and functionalized solid particles dispersed in the polymer matrix.

An advantage of the invention is that it allows the polymer matrix to beselected based primarily on its diffusion properties, strength,stability and other physical characteristics, independent of limitationsand compromises that arise when attempting to synthesize polymers havingspecific types of sensory groups chemically bound to the polymer.Another advantage is that a single polymer matrix or relatively fewdifferent polymer matrices may be used to prepare a diverse sensor arrayusing different fillers. Also, the ability to modify a solid particulateto produce a variety of different types of sensory filler materialsallows certain types of sensors to be fabricated more easily and at alower cost.

These and other features, advantages and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims and appendeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a reaction scheme showing synthesis of thepolymethylphenylcarbosilane of Example 1.

FIG. 2 is a reaction scheme showing preparation of theocta-[propyl-(bis(-4-hydroxyphenyl)hexafluoropropane)] POSS (2) ofExample 2.

FIG. 3 is a reaction scheme showing preparation of themono-[1-(4-hydroxy-4-trifluoromethyl-5,5,5-trifluoro)pentene]hepta(isobutyl)POSS (4) shown in Example 4.

FIG. 4 is a reaction scheme showing preparation of the mono-bisphenol-APOSS (5) of Example 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term “composite” as used herein refers to a composition comprisingat least two distinct immiscible phases, including a continuous phase ormatrix, and a dispersed phase. These distinct phases distinguish thecomposite from a solution which is free of distinct phases andimmiscible components. The expression “solid particulate filler” as usedherein refers to a dispersed phase that is a solid material at normalambient conditions.

The matrix used for preparing the composite sensor coatings of thisinvention preferably include a polymer having a relatively low glasstransition temperature, i.e., a glass transition temperature that ispreferably at about room temperature (22° C.) or below room temperature.The matrix polymer may have any molecular architecture. Suitable matrixpolymers include linear polymers, branched polymers, hyperbranchedpolymers, combburst polymers, dendrons, dendrimers, cross-linkedpolymers, etc. Specific examples of suitable matrix polymers include,but are not limited to, linear, branched and hyperbranchedpolycarbosilanes, polycarbosiloxanes, polycarbosilazenes, andpolysiloxanes.

The functionalized particles dispersed in the polymer matrix may beprepared from solid particulates of the type generally referred to asfillers. Examples of suitable functionalizable particles include variousclays, synthetic fibers such as nylon fibers, aluminum hydroxide,calcium silicate, zinc oxide, carbon fiber, glass fiber, silica,alumina, alumina-silica, carbon black, carbon nanotubes, fullerene,silsesquioxanes, and the like. Each of these materials has hydroxyl orother functional groups that can be reacted with a molecule having asensory moiety to form a functionalized sensory particle that may bedispersed in a polymer matrix. The solid particles or fillers used inthis invention may have an average particle size in the range from aboutone nanometer to several hundred micrometers. However, smaller particlesare preferred, particularly those in the range from about 1 nm to about1000 nm, in order to achieve better, more uniform dispersion of theparticles in the matrix.

Preferred solid filler particles for use in the invention includepolyhedral oligomeric silsesquioxanes (POSS). The POSS particles have arigid, closed-cage siloxane (SiO) structure. Methods of preparingvarious POSS structures are well known. For example, polyhedraloligomeric silsesquioxanes having hydridosilyl (SiH), vinyl, allyl,thiol, amine, haloalkyl, and other reactive functional groups arecommercially available and/or described in the literature. Thesereactive functional groups may be reacted with various compounds havingsensory functional groups to form sensory group functionalized solidparticles that are capable of being uniformly dispersed in a polymermatrix.

The term “silsesquioxane” is used herein to describe a large family ofsubstances including fully-condensed silsesquioxane frameworks (i.e.,those without any remaining hydrolyzable groups) andincompletely-condensed frameworks having reactive Si—OH groups which arepotentially capable for forming additional Si—O—Si linkages viaelimination of water. The term “silsesquioxane” is also used herein todescribe heterosilsesquioxanes derived by substitution of a main-group,transition-metal or f-element atom for one or more of the silicon atomsin a silsesquioxane. Heterosilsesquioxanes derived by substitution of ametal atom for one or more of the silicon atoms in a silsesquioxane arealso referred to as metallasilsesquioxanes. The silsesquioxanes exhibitvery good dispersion properties on account of their relatively smallparticle size, typically from about 5 nm to about 10 nm.

Another advantage with the polyhedral oligomeric silsesquioxanes is thatthey have a very high ratio of functional groups to mass.

Various chemistries may be utilized for functionalizing the solid fillerparticles. For example, hydrosilylation reactions may be employed byreacting a vinyl or allyl functionalized polyhedral oligosilsesquioxaneand/or heterosilsesquioxane with a hydrido-silane or hydrido-siloxanefunctionalized compound that also has a sensory functional group or byreacting a hydridosilane POSS with a vinyl or allyl compound containinga sensory functional group. Vinyl and/or allyl functionalized polyhedraloligosilsesquioxanes are commercially available or may be synthesized bytechniques known in the art. As another example, Michael additionreactions may be employed by reacting a commercially availablesilsesquioxane having methylcarboxyl groups with a compound having anamine group and at least one sensory group. Further, functional groupson the solid particles, such as polyhedral oligomeric silsesquioxanes,silica, etc., may be reacted with various linking compounds having atleast one functional group that will react with a functional group onthe solid particle and at least one other functional group that can bereacted with a compound having a sensory moiety. Examples of functionalgroups that may be utilized for linking the solid particles with acompound having a sensory group include hydroxyl, thiol, carboxyl,ester, alkoxy, alkenyl, allyl, vinyl, amino, halo, urea, oxiranyl,aziridinyl, oxazolinyl, amidazolinyl, sulfonato, phosphonato,hydrosilyl, isocyanato, isothiocyanato, and others.

Fullerenes, carbon nanotubes, and the like may be functionalized byreaction of their carbon-carbon double bonds with various sensor-bearingspecies. Glass fiber, silica, and the like have surface SiOH groupswhich can be converted to sensor groups, such as by reaction with avariety of commercially available coupling agents of the form(RO)_(x)R′_(3-x)Si(CH₂)_(y)X, where SiOR reacts with SiOH, x is zero, 1,2 or 3, y is a positive integer, and X is a functional group such as (anepoxy, amine, acrylate, isocyanate, etc.) to which appropriate sensorgroups can be attached.

Silicon-containing polymers, including hyperbranched polymers, areparticularly useful for use as the matrix polymer for the chemicalsensor applications of this invention due to their low glass transitiontemperature, excellent processability, ease of film formation, inertnessand stability. The presence of a high proportion of silicon-carbonand/or silicon-oxygen bonds in the backbone of the silicon-containingpolymers imparts very low polarity and very low bias polarity and lowglass transition temperature. The silicon-containing polymers may beeasily prepared using hydrosilylation chemistry for polymer synthesisand, if desired, for subsequent cross-linking.

The matrix polymer may include chemically sensitive functional groups(sensory groups) that are the same as those on the sensoryfunctionalized solid particulate fillers distributed through the polymermatrix, i.e., both the matrix polymer and the particulate filler mayinclude the same sensing group that responds to a particular analyte ofinterest. Alternatively, the matrix polymer may be inert to the analyteof interest, with only the functionalized solid particulate fillerresponding to the analyte.

The sensory groups linked to the solid particulate filler, andoptionally to the matrix polymer, may be selected from a wide variety offunctional groups that are commonly employed for detecting analytes ofinterest. Examples of sensory functional groups that may be bound to thesolid particulate fillers include silanol, dihydroxypyrimidine,hydantoin, phenols, halogenated alcohols, oxime, boronic acid,thioxamide, thiol, and succinimide groups.

Chemically sensitive (sensory) functional groups are functional groupsthat are capable of interacting with an analyte of interest (e.g., achemical vapor). Interaction of the functional groups with the analyteresults in a change in a measurable property or characteristic (e.g.,electrical resistance, mass, etc.) of the composite material. Suchinteractions include chemical bonding, dipole-dipole interactions,chemical adsorption, physical adsorption, and the like.

Preferred chemically sensitive functional groups include hydrogen bondacidic groups such as phenolic and alcoholic alkyl (hydroxy alkyl)groups, especially fluorinated phenols and fluorinated alcoholic alkyls.Hydrogen bond acidic functional groups play an important role in thedetection of certain analytes, particularly nerve agents and explosives.Further, hydrogen bond acidic functional groups are important tooptimizing the chemical diversity of an array of polymer coated sensingelements. Other preferred sensory functional groups include hydrogenbond basic groups such as amine, ether, cyano (CN), nitrogen and oxygenheterocycles (e.g., pyridine, pyrimidine, pyrrole, furan, and others),groups containing phosphorous-oxygen double bonds (e.g., phosphonates),moieties containing sulfoxide (—S═O) groups, moieties containing sulfone(—S)═O₂ groups, moieties containing nitroso (NO) groups, and moietiescontaining nitro (NO₂) groups.

Chemical sensors prepared in accordance with an aspect of this inventioncomprise a composite sensory or detector material which includes apolymer matrix and sensory functionalized solid particulate fillermaterial dispersed throughout the matrix. The composite sensory materialis utilized in combination with a transducer element that is capable ofdetecting a change in the composite material due to an interaction withan analyte and generating a signal to indicate the change.

Suitable transducers include any device or mechanism that is capable ofdetecting any change in a physical (e.g., mass, electrical resistance,etc.), chemical (e.g., color change), or physical-chemical property ofthe coating material due to interaction of the coating material with ananalyte and providing a signal indicative of the interaction, and henceindicating the presence and/or quantity of analyte contacting thecomposite sensory material. Suitable transducer elements include, butare not limited to, quartz crystal microbalance, surface acoustic wavedevices, flexural plate wave devices, chemiresistor transducers, andcolorimetric transducers.

In general, the composite sensory materials of this invention areprepared by uniformly dispersing a sensory functionalized solidparticulate filler material in the polymer matrix material. This can beachieved using any suitable technique, such as melt blending orhomogeneously mixing the functionalized solid particulate fillermaterials with monomers, other liquid phase polymer precursors, orpolymers, and subsequently curing or otherwise solidifying the monomersor polymer precursors to form a polymer matrix.

The composite sensor materials of the invention may be coated onto asurface of a transducer element such as a quartz crystal microbalance orsurface acoustic wave device using conventional coating techniques, suchas spray coating, dip coating, brushing, spin coating, solvent casting,etc. In addition to the previously mentioned coating techniques, thecomposite sensory materials of this invention may be applied to asubstrate by various other methods selected from, but not limited to,chemical vapor deposition, vacuum deposition, solution casting, micro-and sub-micro-emulsion spritzing, rapid expansion of super criticalfluids, pulsed laser evaporation, matrix assisted pulsed laserevaporation, etc. Examples of other devices on which the compositesensory materials of this invention may be coated include opticalwaveguide devices, optical fiber-based devices, dip-in or apply-to testkits, etc.

The amount of sensory functionalized solid particulate filler materialutilized in the composites of this invention may vary greatly dependingon a variety of factors, including the analyte or analytes to bedetected, the type of transducer utilized, the characteristics of thematrix polymer, the particular type of sensory groups bound to the solidparticulate filler, and the characteristics of the solid particulatefiller. In general, the amount of sensory functionalized solidparticulate filler material utilized in the composites of this inventionare selected to achieve an optimal balance between response sensitivity(which increases with higher filler loading) and diffusive properties(which tend to diminish with higher filler loading). However, suitablefiller loadings tend to be in a range from about 5% by weight to about50% by weight, and more typically from about 10% to about 25% by weight.

The composites of this invention exhibit improved mechanical propertiesas compared with conventional sensor materials, including betterstrength properties and better aging performance (i.e., long termretention of mechanical and sensing properties). The composites of thisinvention also allow lower cost production of a variety of differentsensor types (i.e., sensors responsive to different analytes) using thesame matrix polymer with different functionalized fillers.

The invention is further illustrated by the following non-limitingexamples.

EXAMPLES Example 1 Polymethylphenylcarbosilane-C6 (1) Matrix Polymer

A 25 mL one-necked round-bottomed flask was equipped with a Tefloncoated magnetic stirrer bar and a condenser with a nitrogen inlet at itstop. The flask was charged with 1.647 g methylphenylsilane (13.4 mmol),1.107 g 1,6-hexadiene (13.4 mmol), 10 mL toluene and one drop ofplatinum divinyltetramethyldisiloxane complex in xylene. The mixture wasstirred at room temperature for 5 days and then stirred with activatedcharcoal at room temperature for 24 hours. The charcoal residue wasremoved by gravity filtration and the toluene was evaporated to give thepolymeric product (synthesized in accordance with the reaction schemeshown in FIG. 1) as an oil in quantitative yield. ¹H NMR (CDCl₃): δ(ppm) 0.23 (s; SiCH₃), 0.73 (m; SiCH₂), 1.27-1.35 (2 m; SiCH₂CH₂,Si(CH₂)₂CH₂), 7.34 (m; ArH), 7.48 (m; ArH). ¹³C NMR (CDCl₃): δ (ppm)−5.1 (SiCH₃), 14.1 (SiCH₂), 23.7 (SiCH₂CH₂), 33.2 (Si(CH₂)₂CH₂), 127.6(ArC), 128.6 (ArC), 133.8 (ArC), 138.9 (ArCSi). GPC (THF as elutant):M_(w)=15875, M_(n)=10205, polydispersity=1.56. DSC; T_(g)=−49° C.

Example 2 Octa-[Propyl-(Bis(−4-Hydroxyphenyl)Hexafluoropropane)] POSS(2)

A 10 mL one-necked round-bottomed flask was equipped with a Tefloncoated magnetic stirrer bar and a condenser with a nitrogen inlet at itstop. The flask was charged with 0.070 g octasilane-POSS (0.069 mmol),0.208 g 2-(3-allyl-4-hydroxyphenyl)-2-(4-hydroxyphenyl)hexafluoropropane(8 equivalents, 0.552 mmol), 4 mL toluene and one drop of platinumdivinyltetramethyldisiloxane complex in xylene. The mixture was heatedat 80° C. for 24 hours and then stirred with activated charcoal at roomtemperature for 24 hours. The charcoal residue was removed by gravityfiltration and the toluene was evaporated to give the product(synthesized in accordance with the reaction scheme shown in FIG. 2) asa white solid in quantitative yield. IR (thin film): ν (cm⁻¹) 3406 (OH),2959, 2926, 2869 (CH₂), 1611 (Ar), 1513 (Ar), 1436 (Ar), 1380 (CF₃),1253 (SiCH₃), 1204 (SiCH₂), 1168, 1090 (SiOSi). ¹H NMR (CDCl₃): δ (ppm)0.10 (s; SiCH₃), 0.88-0.94 (t; SiCH₂), 1.83-1.88 (m; SiCH₂CH₂),2.54-2.56 (t; ArCH₂) 6.79-6.82 (m; ArH), 6.97-7.00 (m; ArH), 7.06 (s;ArH). ¹³C NMR (CDCl₃): δ (ppm) 1.0 (SiCH₃), 18.1 (SiCH₂), 29.7(SiCH₂CH₂), 33.3 (ArCH₂), 114.9, 122.3, 125.3, 128.2, 129.1, 131.7,137.9 (ArC, CF₃, C(CF₃)₂). MALDI-TOF MS (dihydroxybenzoic acid matrix):m/z 4087 (Calc. 4026), 3711 (Calc. 3650).

Example 3 Octa[Propyl-2-Phenol] POSS (3)

A 10 mL one-necked round-bottomed flask was equipped with a Tefloncoated magnetic stirrer bar and a condenser with a nitrogen inlet at itstop. The flask was charged with 0.200 g octasilane-POSS (0.196 mmol),0.210 g 2-allylphenol (8 equivalents, 1.57 mmol), 3 mL toluene and onedrop of platinum divinyltetramethyldisiloxane complex in xylene. Themixture was heated at 80° C. for 24 hours and then stirred withactivated charcoal at room temperature for 24 hours. The charcoalresidue was removed by gravity filtration and the toluene was evaporatedto give the product as a white solid in quantitative yield. IR (thinfilm): ν (cm⁻¹) 3444 (OH), 2954, 2924, 2861 (CH₂), 1590, 1505, 1486,1449 (Ar), 1250 (SiCH₃), 1172, 1087 (SiOSi). ¹H NMR (CDCl₃): δ (ppm)0.12 (s; SiCH₃), 0.64-0.70 (t; SiCH₂), 1.62-1.76 (m; SiCH₂CH₂),2.59-2.64 (t; ArCH₂) 6.73-7.33 (4 m; ArH). ¹³C NMR (CDCl₃): δ (ppm) 1.2(SiCH₃), 17.6 (SiCH₂), 23.5 (SiCH₂CH₂), 33.6 (ArCH₂), 115.5 (ArCH),121.0 (ArCH), 127.2 (ArCH), 128.6 (ArCH), 130.5 (ArCCH₂), 138.1 (ArCOH).²⁹Si NMR (CDCl₃): δ (ppm) 15.6 (OSiMe₂CH₂). MALDI-TOF MS(2,4,6-trihydroxyacetophenone monohydrate matrix): m/z 2117 (Calc.2090).

Example 4Mono-[1-(4-Hydroxy-4-Trifluoromethyl-5,5,5-Trifluoro)Pentene]Hepta(Isobutyl)POSS (4)

A 300 mL steel Parr bomb reactor with a glass liner was charged with0.28 g monoallyl isobutyl POSS (0.327 mmol). The reactor was purged andthen charged with 17.73 g hexafluoroacetone (0.106 mol, approximate300-fold excess). After 24 hours at 90° C. excess hexafluoroacetone waspumped out of the reactor and destroyed by bubbling through anappropriate quantity of sodium borohydride solution in triglyme. Theproduct (prepared as shown in FIG. 3) was isolated by removal fromreactor. IR (thin film): ν (cm⁻¹) 3600 (free OH), 3489 (hydrogen-bondedOH), 2956, 2911, 2867 (CH₂), 1379 (CF₃), 1279, 1209, 1146, 1054 (SiCH₂).¹H NMR (CDCl₃): δ (ppm) 0.58-0.63 (m; SiCH₂), 0.92-0.95 (d; CHCH₃),1.78-1.90 (m; CH(CH₃)₂), 2.75-2.95 (2 d; SiCH═CHCH₂C(CF₃)₂OH cis andtrans), 5.69-6.12 (2 m; SiCH═CHCH₂C(CF₃)₂OH), 6.29-6.48 (2 m;SiCH═CHCH₂C(CF₃)₂OH). ¹³C NMR (CDCl₃): δ (ppm) 22.2, 23.8, 25.6(^(i)BuC), 33.4 (CH₂C(CF₃)₂OH cis), 37.0 (CH₂C(CF₃)₂OH trans),117.1-140.9 (septet, C(CF₃)₂), 129.9 (SiCH═CHCH₂C(CF₃)₂OH cis), 131.2(SiCH═CHCH₂C(CF₃)₂OH trans), 139.9 (SiCH═CHCH₂C(CF₃)₂OH trans), 141.2(SiCH═CHCH₂C(CF₃)₂OH cis). ²⁹Si NMR (CDCl₃): δ (ppm) −64.1, −64.6(O₃SiCH). MALDI-TOF MS (2,4,6-trihydroxyacetophenone monohydratematrix): m/z 1059 (Calc. 1024).

Example 5 Mono-Bisphenol-A POSS (5)

A 100 mL one-necked round-bottomed flask was equipped with a Tefloncoated magnetic stirrer bar and a condenser with a nitrogen inlet at itstop. The flask was charged with 2.54 g monosilane-POSS (3.11 mmol, 2equivalents), 0.480 g 2,2′-diallyl bisphenol-A (1.56 mmol, 1equivalent), 30 mL toluene and one drop of platinumdivinyltetramethyl-disiloxane complex in xylene. The mixture was heatedat 80° C. for 6 days and then stirred with activated charcoal at roomtemperature for 24 hours. The charcoal residue was removed by gravityfiltration and the toluene was evaporated to give a mixture of threeproducts. The product (prepared as shown in FIG. 4) with the highest OHcontent was isolated by flash column chromatography (1:2 v/vdichloromethane-hexane, gradient to 100% dichloromethane);2-(propyl-POSS)-bisphenol-A, 0.24 g product. Rf=0.45 (CH₂Cl₂). IR (thinfilm): ν (cm⁻¹) 3615 (free OH), 3541 (hydrogen-bonded OH), 2956, 2926,2904, 2874 (CH₂ and CH₃), 2630, 1804, 1605, 1497, 1457, 1398, 1379,1364, 1327, 1261 (SiCH₂), 1228 (SiCH), 1109 (SiOSi), 1036, 836 (SiOSi).¹H NMR (CDCl₃): δ (ppm) 0.61-0.66 (m; SiCH₂ and iBu), 0.88-1.00 (m;CH₃), 1.64 (s; Ar₂C(CH₃)₂), 1.80-1.93 (CH(CH₃)₂), 2.51-2.57 (t; ArCH₂),6.09-6.22 (m; ArH), 6.82-7.00 (m; ArH), 7.30 (d; ArH). ²⁹Si NMR (CDCl₃):δ (ppm) −63.0, −61.0 (O₃SiCH). MALDI-TOF MS(2,4,6-trihydroxyacetophenone monohydrate matrix): m/z 1129 (Calc.1085).

Example 6 Initial SAW Responses

Compositions were prepared by uniformly blending the polycarbosilane ofExample 1 with each of the four fillers from Examples 2-5 in the amountindicated in the following table. The resulting composites were coatedonto a 500 MHz surface acoustic wave (SAW) substrate (transducerelement) to form a chemical sensor. The composite surface of thechemical sensors were each exposed to a flowing gas containing 0.5 gramsper cubic meter of dimethyl methylphosphonate (DMMP) (a chemicalcompound commonly employed for testing purposes to simulate a nerveagent) for a period of 5 minutes. The excellent SAW responses are shownin the table. A control experiment in which a SAW substrate was coatedwith pure polycarbosilane (1) gave no significant SAW response with DMMPvapor.

SAW response Matrix Filler (Hz) 85% Polycarbosilane (1) 15% POSSCompound (2) 910 85% Polycarbosilane (1) 15% POSS Compound (3) 1294 80%Polycarbosilane (1) 20% POSS Compound (4) 1165 85% Polycarbosilane (1)15% POSS Compound (5) 1200

The above description is considered that of the preferred embodimentsonly. Modifications of the invention will occur to those skilled in theart and to those who make or use the invention. Therefore, it isunderstood that the embodiments shown in the drawings and describedabove are merely for illustrative purposes and not intended to limit thescope of the invention, which is defined by the following claims asinterpreted according to the principles of patent law, including thedoctrine of equivalents.

1. A composite material for sensing an analyte, comprising: a polymermatrix; and a solid particulate filler dispersed in the polymer matrix,the solid particulate filler having functional groups capable ofinteracting with the analyte, and wherein the solid particulate filleris a functionalized polyhedral oligomeric silsesquioxane.
 2. Thecomposite material of claim 1, in which the polymer matrix includes apolymer having a glass transition temperature at about room temperatureor below room temperature.
 3. The composite material of claim 1, inwhich the solid particulate filler is functionalized with hydrogen bondacidic groups.